Genes and mRNAs coding for histones can be isolated from sea urchins. These genes may represent as much as 0.25% of the total DNA as there are up to several hundred to 1000 copies of each histone gene in addition to interspersed spacer DNA. The genes coding for the five histone proteins are all arranged within a repeating structure of about 6 Kb. Our objectives are two-fold: 1) To learn more about the organization and fine structure of the histone genes, 2) To investigate the transcription of this DNA both in vivo and in vitro. The analysis of the fine structure includes a determination of the variations between the repeat units with measurements of spacer size and position in the units of various lengths. We will also try to determine whether any of the genes in the kb repeat codes for histones of variant sequence. We will employ the techniques of restriction enzyme mapping, cloning of recombinant plasmids and electron microscopic analysis. Transcriptional studies include a search for precursors to histone DNA, development of an assay system to determine factors which aid in proper initiation of the histone transcripts, and identification of proteins which bind selectively to the histone genes. The isolated histone DNA can be used as a hybridization probe for newly synthesized histone mRNA sequences, thus allowing the determination of synthetic rates for each of the histone mRNAs in the developing sea urchin embryo.